The progressive loss of CD4 lymphocytes correlates with the progression of HIV infection to AIDS. At present, other correlates of disease progression are lacking. Thus, routine immunophenotyping of HIV-infected individuals is justified. Unfortunately, analysis of other lymphocyte markers has not been sufficiently done to determine if they also can predict changes in the course of the disease. The immune system is a complex interaction of many cell types. A progressive decline in the CD4 lymphocyte compartment is likely to cause shifts in the proportions of other lymphocyte subsets. The question arises as to whether changes in other lymphocyte surface antigens correlate with disease progression and more ideally, stabilize or revert in response to efficacious drug therapy. In order to investigate this issue, single color immunofluorescence technology had to develop a dual color capability. With the use of 2-color immunofluorescence, some activation and differentiation markers on lymphocyte subset cells showed promise of being good correlates of disease progression. However, these markers were not investigated in the context of clinical trials to assess drug effectiveness. A major reason was the cost and time required to analyze an extensive panel of 2-color profile tubes. Recently a third fluorochrome for routine 3-color immunofluorescence has become commercially available. The proposed study hopes to utilize this newest technology to consolidate a number of 2-color profile tubes into a more limited panel of 3-color profile tubes. This would allow a more manageable evaluation of clinical specimens. In addition, combinations of 3 discrete antibodies to pinpoint a particular subpopulation of lymphocytes can now be routinely investigated. One of the goals of this research will be to validate and justify the switch from routine 2-color to 3-color analysis. This will enable a more aggressive analysis of lymphocytes from individuals enrolled in ACTG clinical trials using an expanded panel of 3-color analysis tubes. It is hoped that in the subsequent years of this project, routine 3-color immunophenotyping will identify and validate changes in lymphocyte subset markers that correlate with HIV disease progression and/or drug efficacy.